Catabolic genes of soil bacteria offer a unique system for studying fundamental processes of procaryotic gene regulation. The main objective of this research is to explore the divergence in a pool of structural genes encoding substituted aromatic compound catabolism. We propose to characterize and clarify the role of enzymes strategically located in a metabolic route in extending the phenotypic capabilities of bacterial hosts. We will examine the contribution of these strategic enzymes to the utilization of fossil, renewable, and synthetic compounds. These studies will also enable us to correlate the structure and function of these enzymes. To this end, the structure and regulation of genes encoding chlorocatechol dioxygenases and monooxygenases will be analyzed. Two types of monooxygenases of our interest are salicylate hydroxylase and 2,4-D monooxygenase. Another objective is to study bacterial genes that regulate catabolic pathways governing the oxidation of substituted aromatic compounds to tricarboxylic acid cycle intermediates using complementation, recombinant DNA and other techniques. Regulatory genes controlling chloroaromatic catabolism, tfdR/S and tfdT of 2,4-dichlorophenoxyacetate (2,4-D) and dcbR of 1,4-dichlorobenzene degradation, will be dissected at the molecular level. The role of the proteins encoded by three 2,4-D regulatory genes will be examined. The third objective is to investigate the action mechanisms of single and multiple regulatory elements and the molecular details of the partial expression of convergent pathways for 2,4-D and 1,4-dichlorobenzene catabolism.